One of the most unnerving things about modern communications technology is the way devices constantly leak information about their physical whereabouts—to mobile carriers, network operators, e-mail providers, web sites, governments, even shopping mall owners. Many of these information leakages are simple historical accidents. The designers of technologies never considered that technical standards would let everyone around you notice your device's presence. They never considered that technical choices would let web sites infer when two people are (or aren't) spending the night in the same residence, or let your phone company follow you around virtually from moment to moment.

Massachusetts police must now get a search warrant before they can track a person's past movements through their cell phone in an important new decision that has implications beyond just cell tracking in the Bay State.

In Commonwealth v. Augustine, state police relied on federal law to obtain an order authorizing the disclosure of two weeks worth of historical cell site records from Sprint in connection with a murder investigation. But the order wasn't a search warrant supported by probable cause. Years after obtaining the records and a criminal case was brought against Augustine, a different judge found the police had violated the Massachusetts state constitution when it failed to get a warrant.

Much of the debate over modern surveillance—including the NSA mass spying controversy—has centered around whether people can reasonably expect that records about their telephone and Internet activity can remain private when those records belong to someone else: the service providers. Courts havedisagreed on whether the 1979 Supreme Court case Smith v. Maryland, which ruled people have no expectation of privacy in the phone numbers they dial, should be extended to cover newer, more invasive forms of technology.

As the year draws to a close, EFF is looking back at the major trends influencing digital rights in 2013 and discussing where we are in the fight for free expression, innovation, fair use, and privacy. Click here to read other blog posts in this series.

The historicdecision handed down by D.C. federal judge Richard Leon last week that found the NSA's bulk collection of phone records likely violated the Fourth Amendment is a crucial first step towards protecting digital privacy from suspicionless government searches. But the importance of the decision extends beyond the NSA's surveillance programs. Judge Leon made two important findings on how the Fourth Amendment right to be free from unreasonable searches should apply at a time when technology can make invasive surveillance -- once considered the stuff of science fiction -- a part of every day life.